The fart test is a test of the closeness of one's relationship to another. If one is comfortable farting in front of others it means that they are close to that person and they have a good relationship with one another.You can tell how close you are with another depending if you hold in a fart around them or if you let it out without giving a shit.

The Fart Test can distinguish the relationship between two people such as
gfs farting in front of the bfs
best friends farting in front of one another